Adaptive E-drive operation for electrified vehicle

ABSTRACT

A system is configured to receive vehicle state input, and in response to the vehicle state input, select an operational mode for PWM switching of electronics in a power conversion circuit of a hybrid electric vehicle electric drive system (EDS). Vehicle state input can pertain to EDS state, engine state, and the presence of alternative noise sources, such as audio equipment, climate control equipment, and lowered windows. Various operational modes can include a noise reduction mode in which EDS noise is reduced, a loss reduction mode in which EDS losses are reduced, and a default mode, which can be designed to maximize fuel efficiency. A system can be configured to provide a PWM implementation strategy based on operational mode selection. By way of example, a PWM implementation strategy can comprise random PWM, continuous PWM, discontinuous PWM and fixed frequency PWM.

CROSS-REFERENCE TO RELATED APPLICATIONS

This continuation application claims priority from parent U.S.application Ser. No. 12/686,355 filed on Jan. 12, 2010, which isincorporated herein in its entirety by reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to electric drive systems. In particular,the invention pertains to pulse width modulation (PWM) strategiesemployed at an electric drive system.

2. Background Art

Electric machines, in particular electric or hybrid electric vehicles,may employ electrical energy for propulsion via an electric drivesystem. An electric drive system can encompass a number of components,typically including at least a power circuit and a motor. In thisarrangement, the power circuit can controllably transfer power from apower source to the motor to drive a load. Power circuits for electricdrive systems designed for electric or hybrid electric vehicles ofteninclude inverters for providing three-phase voltage waves from a dcvoltage source. Typically an inverter is composed of a plurality ofelectronic switches that are controllably turned off and on in variouscombinations to provide desired inverter output voltages.

It is common practice to use pulse width modulation (PWM) techniques toturn the switches on and off. The rate at which the switches are turnedon and off is typically determined by motor speed or torque requirementsas well as fuel efficiency considerations. Unfortunately, in many cases,switching the various electronic devices on and off at a particularfrequency can generate noise audible to the vehicle driver, as well ashis passengers. The noise can be distracting and irritating, and isoften the subject of consumer complaints.

Various attempts have been made to reduce or eliminate irritating PWMswitching noise at an electric vehicle. For example, PWM switching canbe performed at a higher frequency, such as 10 kHZ, which is outside thehuman audible range. However, this solution has its disadvantages. Whilethe higher switching frequency no longer generates noise heard by theoperator, it induces power losses in the system that can reduce fueleconomy, a long-standing priority for hybrid vehicles, and increasepower circuit costs.

SUMMARY OF INVENTION

An example system includes a pulse width modulation (PWM) frequencyadaptation mechanism (PFAM) configured to receive vehicle state input,and in response to the vehicle state input, select a PWM operationalmode to be implemented at a vehicle electric drive system. The vehiclestate input can pertain to additional sources of noise at a vehicle thatcan mask noise produced by an electric drive system at the vehicle.Possible noise sources include auxiliary systems such as an audiosystem, a climate control system, lowered windows, an engine, etc. Inaddition to auxiliary equipment, vehicle state input can also includeinput regarding engine and electric drive state. A system can furtherinclude an apparatus coupled to the PFAM and configured to implement theselected PWM operational mode. By way of example, operational modes caninclude a noise reduction mode, a loss reduction mode, and a defaultmode. For example, when noise that can mask the sounds of an electricdrive system is present, a default mode can be implemented, while in theabsence of alternative noise sources, a noise reduction mode can beimplemented. A PFAM can be configured to provide a PWM implementationstrategy based on the selected operational mode. By way of example, aPWM implementation strategy can include continuous PWM, discontinuousPWM, random PWM or fixed frequency PWM. In an example embodiment, a PFAMcan be configured to receive user input in addition to vehicle stateinput, and an operational mode can be selected based on both vehiclestate input and operator preference input.

The invention departs from the conventional practice of using motorspeed torque requirements to select a PWM switching frequency thatcharacterizes electric drive operation. Instead, the inventiondynamically adapts electric drive operation by using various vehicleinputs to select an operational mode directed to achieve an objectivesuch as to reduce noise, reduce loss, or optimize fuel usage. A systemcan further include an apparatus configured to implement the providedPWM strategy, such as a power conversion circuit configured to providean output voltage using electronic devices that are switched on or offby pulse width modulation implemented in accordance with the PFAMoperational mode and PWM strategy.

In an example embodiment, a PFAM can be embodied as a software moduleembedded at a microprocessor or other digital processing device at avehicle. For example, a system can include a digital processor and acomputer readable medium operatively coupled to the digital processor,having stored thereon logic for sequences of instructions for thedigital processor. The sequence of instructions, when executed by thedigital processor cause the processor to select a PWM operational modebased on vehicle state input.

An example method can include receiving vehicle state input, andselecting a PWM operational mode based on the received vehicle stateinput. For example, a method can comprise receiving vehicle motioninput, receiving engine state input, receiving ventilation system stateinput, receiving audio system state input, receiving vehicle body stateinput, and determining an operational mode in response to the receivedinput. A method can further include receiving user input and selectingan operational mode based on vehicle state input and user input. Amethod can comprise selecting a noise reduction mode when alternativesources of noise are absent, and selecting a default mode whenalternative noise sources are present to mask the noise produced by anelectric drive system. A method can include implementing a lossreduction mode when a vehicle state input indicates that an electricdrive system is heavily loaded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a vehicle equipped with a PWM FrequencyAdaptation Mechanism (PFAM).

FIG. 2 is a block diagram of an example vehicle control system.

FIG. 3A shows a block diagram of an example embodiment.

FIG. 3B depicts a block diagram of an example embodiment.

FIG. 4 shows a flow diagram of an example method of the invention.

FIG. 5 depicts a block diagram of an example apparatus.

FIG. 6 depicts a flow diagram of an example method.

FIG. 7 shows a flow diagram of an example method.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments of the invention are presented herein; however, theinvention may be embodied in a variety of alternative forms, as will beapparent to those skilled in the art. To facilitate understanding of theinvention, and provide a basis for the claims, various figures areincluded in the description. The figures are not drawn to scale andrelated elements may be omitted so as to emphasize the novel features ofthe invention. Structural and functional details depicted in the figuresare provided for the purpose of teaching the practice of the inventionto those skilled in the art and are not to be interpreted aslimitations. For example, control modules for various systems can bevariously arranged and/or combined, and are not to be considered limitedto the example configurations presented herein.

FIG. 1 illustrates a schematic of an example vehicle 100. The vehicle100 may be of any suitable type, such as an electric or hybrid electricvehicle. In at least one embodiment, the vehicle 100 may include a firstwheel set 112, a second wheel set 114, an engine 116, an HEV transaxle118, an electric drive system (EDS) 120, a power transfer unit 130, adifferential 140, and a vehicle control system (VCS) 150.

The EDS 120 may be configured to provide torque to the first and/orsecond wheel sets 112, 114. For example, the EDS 120 may include a highvoltage battery (HVB) 122 and a power electronics converter (PEC) 121coupled to one or more Permanent Magnet Synchronous Machines (PMSM) 126.The PMSM 126 can be coupled to the power transfer unit 130 or HEVTransaxle 118, which in turn can be coupled to the differential 140 tocontrol the wheel set 114. It is contemplated that the PMSM 126 canfunction as a motor, converting electrical energy to kinetic energy, oras a generator, converting kinetic energy to electrical energy.

The power transfer unit 130 may be selectively coupled to at least onePMSM 126. The power transfer unit 130 may be of any suitable type, suchas a multi-gear “step ratio” transmission, continuously variabletransmission, or an electronic converterless transmission as is known bythose skilled in the art.

The power transfer unit 130 may be adapted to drive one or more vehiclewheels. In the embodiment shown in FIG. 1, the power transfer unit 130is connected to a differential 140 in any suitable manner, such as witha driveshaft or other mechanical device.

In an example embodiment, the PEC 121 includes an inverter systemcontrol (ISC) 123 comprising hardware, including inverter circuitry,configured to provide power to the PMSM 126. An ISC controller 124 canbe coupled to the ISC 123. The ISC controller 124 can be amicroprocessor-based device configured to control operation of the ISC123, and comprise hardware, software, firmware or some combinationthereof. In an example embodiment, currents and voltages of the ISC 123can be controlled by controllably switching ISC circuit elements usingpulse width modulation.

The ISC controller 124 may be electrically coupled to the VehicleControl System (VCS) 150 which is configured to monitor and/or controlvarious aspects of the vehicle 100. The VCS 150 can comprise a VCScontroller communicatively coupled to one or more control modules forone or more various systems installed at a vehicle, and/or to sensorsassociated with various vehicle systems, and/or to various vehiclecomponents or sensors. FIG. 2 provides an example embodiment 200 of aVCS. The VCS 200 includes a VCS controller in the form of a VCS controlmodule (VCSM) 202, coupled to an engine control module (ECM) 204 forproviding engine control and monitoring engine state, a climate controlmodule (CCM) 204 for controlling vehicle interior temperature andventilation system state, an audio system control module (ASCM) 206 forcontrolling and/or monitoring audio system operation, and a body controlmodule (BCM) 210 for controlling and/or monitoring aspects of thevehicle body, such as, but not limited to window operation and state.The VCSM 202 can also be communicatively coupled to one or more sensors,such as vehicle speed sensor 212.

In an example embodiment, the VCSM 202 can be in the form of amicroprocessor or microcontroller configured to communicate with thevarious control modules depicted in FIG. 2, as well as other controlmodules or sensors not shown. The group of control modules depicted inFIG. 2 is not exhaustive, but rather is focused on the components mostpertinent for teaching the invention. For example, a VCS can alsoinclude a transaxle control module for controlling torque provided tovehicle traction wheels, high voltage battery control module forcontrolling operation of a high voltage battery, a traction batterycontrol module for monitoring environmental attributes such astemperature, and controlling one or more power sources, a powertraincontrol module, and other modules associated with various other vehiclesystems. Further, it is contemplated that one or more systems, by way ofexample but not limitation, a vehicle audio system, may not becontrolled by a specific module or controller, in which case a VCSM orVCS controller may receive system state input via a sensor or directconnection with a system component. It is noted that functionsassociated with the control modules and/or sensors depicted in FIG. 2can be variably combined and/or performed at other vehicle modules orcomponents.

As shown in the example system 100, a PWM Frequency Adjustment Mechanism(PFAM) 125 can be coupled to the ISC controller 124 and the VCS 150. ThePFAM 125 can be configured to receive vehicle state input obtained bythe VCS 150, and determine at least one PWM parameter in response to thereceived input. In an example embodiment, the PFAM 125 can provide theat least one PWM parameter to the ISC controller 124, so that the ISC123 can operate under the PFAM 125-designated PWM parameters. The PFAM125 can comprise hardware, software, firmware, or some combinationthereof, and can be embodied as a stand alone unit, or as a moduleincorporated or integrated within an existing vehicular component, suchas a microprocessor device.

FIG. 3A depicts an example embodiment 300 that includes a PFAM 304installed at an ISC controller 302. In an example embodiment, the PFAM304 is in the form of a software module installed and executable at theISC controller 302. The ISC controller 302 is configured to controloperation of the ISC 306. A user input means 308 is coupled to the PFAM304 and configured to receive operator preferences. For example, somevehicle operators may prefer a noise reduction mode in which designatedPWM frequency and strategy reduces PWM switching noise. Other operatorsmay prefer a default operational mode in which PWM parameters areselected without consideration of PWM noise. In an example embodiment,the user input means 308 can be embodied as a button or switch on avehicle dashboard, preferably easily accessible by the vehicle driver,that can be depressed by a user to indicate that noise reduction isdesired. In an example embodiment, the user input means 308 isconfigured to receive user preference input and provide it to the PFAM304.

In an example embodiment, a system can include a PFAM comprising an ISCPFAM portion and a VCS PFAM portion. Referring to FIG. 3B, a system 320can include an ISC 322 coupled to an ISC controller 324. An ISC PFAMportion in the form of an IPFAM module 326 can be installed at the ISCcontroller 324 and be executable thereon. The system 320 can include aVCS 330 having a VCS controller 332, with a VCS PFAM (VPFAM) module 334installed and executable thereon. A user input means 328 can beconfigured to provide user input to the VPFAM module 334.

In an example embodiment the VPFAM 334 can be embodied as a softwaremodule and be configured to receive input regarding a variety of vehiclesystem and apparatus states via the VCS controller 332. For example, theVCS controller 332 can be configured to receive vehicle speedinformation from the vehicle speed sensor 212 and provide it to theVPFAM 334. The VPFAM 334 can be configured to provide vehicle stateinput for the IPFAM 326, for example via the communicative coupling ofthe VCS controller 332 and the ISC controller 324. Thus, the VPFAM 334and IPFAM 326 can cooperate to determine at least one parameter of thePWM practiced at the ISC 322.

FIG. 4 depicts a flow diagram of an example method 400. At block 402vehicle state input can be received at a PFAM. Referring to FIG. 5, anexample PFAM 500 can receive vehicle state inputs 504-512 and provide anoutput 520. In an exemplary embodiment, the various inputs 504-512 arerelated to potential noise sources that can be heard by a vehicleoccupant. In at least one example, input to the PFAM 502 can includeinput 504 pertaining to vehicle motion, input 506 pertaining to vehicleengine state, input 508 pertaining to vehicle climate control systemstate, input 510 pertaining to vehicle audio system state, input 512pertaining to vehicle window state, and input 514 pertaining to EDSstate. In an example embodiment, a VCS provides the inputs 504-512 tothe PFAM 502, while input 514 can be received from a sensor within theEDS 120. Typically, a VCS can obtain the vehicle state data expressed inthe inputs 504-512 from the various vehicle systems to which it iscommunicatively coupled, without requiring additional sensors orhardware.

The vehicle motion input 504 can comprise information characterizing thespeed at which the vehicle is moving. For example, the VSC 150 canprovide speed information from the speed sensor 212 to the PFAM 502. Atthe PFAM 502 vehicle speed may be characterized categorically as lowspeed or high speed, by other general categories, or by quantitativeterms such as miles or kilometers per hour. At high speeds, engine noiseand road noise typically increase and can be louder than the PWM relatednoise, shielding an operator from the sound of the PWM switching.However at low speeds, engine and road noise are typically lower,causing the PWM related noise to be more noticeable by an occupant,particularly a driver, since an ISC is typically located on the driver'sside of a vehicle. In an example embodiment, vehicle motion inputcomprises vehicle shift input which can indicate whether a vehicle is ina drive mode. When a vehicle is in a drive mode, a noise reduction modecan be selected, while when the vehicle is not in a drive mode, adefault mode may be selected.

The engine status input 506 can comprise information pertaining to avehicle engine mode. An engine can operate in several different modes.In an example embodiment, when an engine is an OFF mode, a vehicle canbe driven by an electric motor, necessitating PWM switching of inverterelements that can produce noise that a user may want to avoid.Furthermore, because the engine is in an OFF mode, it is not producingnoise, so cannot mask the PWM switching noise. Thus, when an engine isin an OFF mode, a noise reduction mode can be selected. When a vehicleengine is in a cranking mode, engine-generated noise is typically high,and may mask PWM switching noise. Accordingly, a nominal or default PWMmode may be selected. When an engine is in an acceleration ordeceleration mode, a noise-reduction mode is generally preferred.

Climate control system status input 508 can comprise informationcharacterizing the operation of the vehicle heating/air conditioningsystem(s), another potential source of noise that may shield a driverfrom hearing PWM-related noise. In an example embodiment, climatecontrol system status input 508 comprises data characterizing whetherthe vehicle air conditioner is turned on or is turned off. In a furtherexample embodiment, the input 508 can comprise data characterizingclimate control system fan speed, since a fan can operate to both heatand cool the car. By way of example, but not limitation, fan speed canbe expressed in general categories or by specific speeds. Other ways tocharacterize operation or state of the climate control system will occurto those skilled in the art.

The audio system status input 510 can comprise information pertaining tothe vehicle audio system, for example whether a source is providing anaudio signal to a speaker. A vehicle audio system can include variousaudio/visual equipment such as a radio, compact disc player, mp3 player,video player, and the like which can provide audio signals to one ormore speakers mounted in the vehicle. The audio projected by thespeakers, if sufficiently loud, can hide the noise produced by PWMswitching operations. As an example, audio system input can includecurrent operational status of a vehicle radio.

In an example embodiment, audio system state input can comprise a volumesetting for the speakers of the audio system, which can be used withvarious components of a vehicle's audio/visual system. Typically asingle volume control, such as the volume control knob of a radio, cancontrol speaker volume for a set of one or more speakers. However, whenthis is not the case, for example when a built-in video player has aseparate volume control, or when rear seat passengers have a separatevolume control, audio state input 308 can comprise more than one volumesetting. In addition to a volume setting, audio system input 510 caninclude whether an audio or audio/visual player is actually providing anaudio signal. For example, a CD player may be turned on and a volumecontrol knob turned up, but there may be no CD present, so the CD playerwould not be producing sound.

A lowered window on a vehicle can also be considered a source of noisefor those riding in the automobile. In addition to generating its own“road noise”, an open window can expose an occupant to various soundsand noises outside the vehicle. Window status input 512 includesinformation pertaining to whether one or more vehicle windows islowered; i.e. whether at least one window is open. In an exampleembodiment, window status input 512 can include the degree to which awindow is open and/or identify the open window. For example, a smallvent window open in the rear of a van may cause less driver distractingnoise than a driver's window that is completely lowered.

In an example embodiment, EDS state input 514 can comprise informationthat indicates whether an EDS is fully loaded. By way of example, butnot limitation, input 514 can comprise temperature data from a sensorpositioned at the EDS, for example within the ISO 123 or at the PMSM126. A high temperature reading can indicate that the EDS 120 is fullyloaded, in which case power requirements and/or losses can be consideredin selection of a PWM parameter.

Using the inputs 504-514, the PFAM 502 can determine a PWM parameter atblock 404. A PWM parameter can be any attribute that characterizes orquantifies PWM performance. For example, a PWM parameter can comprise aPWM switching frequency, a PWM strategy, or both. By way of example, butnot limitation, a PWM strategy can comprise a continuous,non-continuous, or random strategy. In the past, PWM frequency has beenselected on the basis of motor state or torque requirement. The presentinvention provides systems and methods for designating a PWM frequencybased on vehicle state information. In an example embodiment, a PWMfrequency can be selected that reduces noise while optimizing ISO andvehicle performance. For example, based on vehicle state input thatindicate that a set of particular conditions are in effect, a PWMfrequency of 7.5 kHz-10.0 kHz can be selected over a default switchingfrequency of 1.25 kHz-5.0 kHz. In an example embodiment, a PWM strategycan be designated that optimizes performance, whether a high or low PWMswitching frequency is specified.

The invention provides a method and system in which vehicle stateinformation can be used to determine whether PWM is performed in anoise-reduction mode or in a default mode. In an example embodiment,when a noise reduction mode is selected, a PFAM provides one or more PWMparameters that can reduce PWM switching noise heard by a driver. By wayof example, but not limitation, when a default mode is selected, pulsewidth modulation is performed without consideration of PWM noiseeffects. For example, PWM parameters can be specified on the basis offuel economy.

FIG. 6 depicts a flow diagram of an example method 600. At block 602 aPFAM can receive user input. For example, the PFAM 502 can receive userpreference input 516. Referring to FIGS. 3A and 5, user input 516 can bereceived via user input means 308 and provided to the PFAM 304. In anexample embodiment, the user input means 308 is in the form of a buttonor switch, or other hardware mechanism that can be manipulated by adriver to indicate a desire for PWM noise reduction. As a furtherexample, user input can be programmed, eliminating the need for ahardware input means, and user preference can be stored in software,either at the PFAM 304, or at another software module in communicationwith PFAM 304. For example, a user preference can be programmed in theVCS controller 332 or at a dashboard information center. In an exampleembodiment, the user preference input 516 comprises an operational modepreference of a driver; for example, whether a noise reduction mode or adefault mode is preferred. Some drivers may pay little or no regard toPWM-related noise, and may actually prefer to hear it. Other drivers mayfind the PWM noise very irritating.

At block 604, vehicle state input can be received. For example, asdiscussed above for block 402 of method 400, input such as that shown inFIG. 5, including vehicle motion input, engine status input, climatecontrol system status input, audio system status input, vehicle bodyinput, and E-drive status input can be received.

At block 606, a PFAM can designate a PWM operational mode based on userpreference and vehicle state inputs. For example, the PFAM 304 canperform an algorithm using the user preference and vehicle state inputsto determine whether pulse width modulation at an ISO should beperformed in a noise reduction mode or in a default mode. In an exampleembodiment, if a user prefers a default mode, a default mode is selectedat the PFAM 304.

A noise-reduction mode and default mode can be variably defined. In atleast one example, a default mode can be characterized by a defaultswitching frequency and/or default PWM strategy, and a noise-reductionmode can be defined as one in which the PWM switching frequency and/orstrategy are different from those of the default mode. As a furtherexample, a default mode can be one in which a PWM switching frequency of5.0 kHz or less is specified by a PFAM, while a noise-reduction mode canbe one in which a PWM switching frequency greater than 7.5 kHz isdesignated. Alternatively, in a default mode a PWM switching frequencywithin the audible band can be employed, while in a noise-reduction modea PWM switching frequency outside the audible band can be employed. As afurther example, a default mode can include a first set of PWMfrequencies and strategies, while a noise-reduction mode can include adifferent set of PWM frequencies and strategies. Other ways ofdistinguishing a default mode from a noise-reduction mode will occur tothose skilled in the art. By way of example, but not limitation, when adefault mode is not preferred by a user or selected by a PFAM, a PWMparameter can be selected that reduces noise or reduces power losses.

At block 608, at least one PWM parameter is specified in accordance withthe selected operational mode. For example, if, based on the receivedinputs 504-514, a noise reduction mode is designated, the output 330 cancomprise a PWM parameter that can reduce the noise generated during PWMswitching. For example, the output 330 can comprise a high PWM switchingfrequency which is less audible than a lower default switchingfrequency. Likewise, the output 330 can comprise a PWM strategy, such asrandom frequency hopping about a specified frequency (whether high orlow) that can reduce the noise perceived by an operator. In an exampleembodiment, the PWM parameter can be provided to an ISO controller thatcontrols ISO operation. For example, the PFAM 212 can designate a PWMstrategy and provide it to the ISO controller 210 so that the ISO 216can implement the designated PWM strategy.

FIGS. 7A and 7B show an example method 700. At block 702, an electricdrive run mode is entered. At decision block 704 a determination is madeas to whether a user prefers a default mode. In an example embodiment, auser can select a preferred operational mode via user input means 328which can provide the user preference to the IPFAM 326. By way ofexample, but not limitation, active selection of a default mode and/orfailure of a user to designate a preferred mode other than a defaultmode, results in selection of a default mode in which a default PWMparameter is selected at block 726. For example, the IPFAM 326 outputcan comprise a predetermined default PWM strategy. In an exampleembodiment, the IPFAM 326 can provide the default PWM strategy to theISC controller 324 so that the default strategy can be implemented atthe ISC 322.

If a default mode is not selected, for example a user indicates apreference for a noise-reduction mode, the method 700 continues withdecision blocks pertaining to the state of various vehicle systems orcomponents. Preferably, vehicle state input comprises status informationfor vehicle components other than a vehicle motor. In an exampleembodiment, when vehicle state information indicates the presence ofnoise from another source, a default PWM parameter is selected. However,if the user selects a noise-reduction mode, and vehicle state inputindicates an absence of other noise, a noise-reduction PWM parameter,rather than a default PWM parameter can be selected.

For example, at decision block 706 a determination is made as to whethera vehicle window is open. As an example, from the VCS controller 310 thePFAM 304 can receive ventilation state input 508 which can include dataregarding the state of the vehicle windows. If at least one window isopen, the PFAM 304 can designate a default PWM parameter as output atblock 726. If no window is open, the example method 700 can proceed todecision block 708 in which a determination is made as to whether thevehicle air conditioner is turned on. For example, the PFAM 125 canreceive ventilation system input 508 which can be in the form ofinformation conveying whether the air conditioner is turned on. Becausean operating air conditioner can produce fan noise that can mask PWMswitching noise, a determination that the air conditioner is on can leadto block 730 at which a default PWM parameter is specified. Pulse widthmodulation characterized by the default PWM parameter can be performedat the ISC 123.

If the air conditioner is not on, the method 700 can proceed to block710 where a determination can be made as to whether the vehicle radio ison. For example, audio system input 510, which can be obtained by theVCSM 202 and provided to the PFAM 304, can comprise informationregarding whether a vehicle radio is turned on. If the radio is turnedon, the example method 700 can proceed to block 726 at which a defaultPWM parameter is selected.

If the radio is not turned on, the method 700 can continue to decisionblock 712 at which a determination is made as to whether the vehicle isin a drive mode. In an example embodiment, this determination is madebased on vehicle shift input provided to a PFAM; for example, vehiclemotion input 504 can comprise vehicle shift input. If the vehicle is notin drive mode, the method 700 can proceed to block 726 at which adefault PWM parameter is specified.

If the vehicle is in drive mode, the method can continue to a decisionblock 714, at which a determination is made as to whether the vehicle isaccelerating or decelerating. The noise due to PWM switching can be morepronounced during periods of acceleration or deceleration; therefore itis generally desirable to select a noise reduction mode during theseperiods. Accordingly, the method 700 can continue to block 716, at whicha noise reduction PWM parameter is selected. By way of example, a noisereduction PWM parameter can comprise a high PWM switching frequency.Also by example, a noise reduction PWM parameter can comprise a PWMstrategy performed using a high PWM switching frequency. A highfrequency can be variably defined. For example, it can be any frequencyhigher than the frequency used for the default frequency at block 726.It can also be defined as a frequency greater than a predeterminedthreshold, or a frequency within a predetermined frequency range.Preferably a high PWM frequency is higher than the band of frequenciesaudible to the human ear. In an example embodiment, a high frequency canbe a frequency higher than 7.5 kHz. In an example embodiment, a PFAMincludes a look-up table of low and high frequencies from which a PWMswitching frequency can be selected. A PWM strategy using the designatedhigh frequency can then be performed at the ISO 123. As an example, arandom PWM strategy using a high frequency can be practiced.

If the vehicle is moving at a constant speed, i.e. neither acceleratingor decelerating, the method can continue to block 718 at which adetermination is made as to whether the vehicle is moving at a lowspeed. Vehicle motion input 504 can comprise vehicle speed informationthat can be received from a vehicle speed sensor, for example vehiclespeed sensor 212. By way of example, but not limitation, a high speedcan be defined as a speed greater than a predetermined threshold. Forexample, a speed greater than 40 mph can be considered a high speed. Ata high speed, the engine typically generates sufficient noise to maskthe sound of PWM switching, so the method 700 can continue to block 726when the vehicle is moving at a high speed. Alternatively, when avehicle is moving at a low speed, the method 700 can continue todecision block 720 at which a determination is made as to whether theelectric drive is heavily loaded. One indication that the electric driveis heavily loaded is that temperature inside an ISO and/or at a PMSMbecomes high. For example, an ISO temperature around 110° C. canindicate that the electric drive is heavily loaded. In an exampleembodiment, the ISC controller 124 can monitor the temperature providedby a sensor within the ISC power stage and/or motor stator windings, andprovide EDS state input 514 to the PFAM 502. By way of further example,the PFAM 502 can directly receive input 514 from a sensor within an EDS.When the electric drive is heavily loaded, use of a high PWM frequencycould cause the ISC to overheat, therefore a loss-reduction PWMparameter can be selected at block 722, such as a low PWM frequencyand/or a random PWM strategy. Although a lower frequency generally isless effective in reducing noise because a lower frequency may still bewithin the audible band of an occupant, the noise effects of a low PWMfrequency can be mitigated by proper selection of a PWM strategy. Forexample employing a random frequency-hopping PWM strategy can spread thepower spectrum over a range of lower frequencies, and thereby reduce thePWM-generated noise. If the electric drive is not heavily loaded, anoise-reduction PWM parameter, such as a noise reduction PWM frequency,for example a high PWM switching frequency, which provides better noisereduction, can be tolerated by the ISC and therefore can be selected atblock 724.

Whether the designated PWM frequency is high or low, selection of a PWMparameter can include selection of a PWM strategy to be implemented atthe ISC 123. As mentioned previously, a PWM strategy can include, butnot be limited to, continuous PWM, non-continuous PWM or random PWM.Random PWM can be implemented by selecting a frequency at random from alook-up table. Alternatively, random PWM can be practiced by frequencyhopping about the designated frequency to diffuse the power spectrum.

Example methods for using vehicle state input to designate one or morePWM parameters for pulse width modulation switching operations at an ISCare presented herein. The use of vehicle state input and/or userpreference input to determine the characteristics of the pulse widthmodulation used at an electric drive system of a hybrid vehicle is incontrast to prior art methods that used motor speed and torquerequirements as a basis for designating PWM switching frequencies,strategies or other PWM characteristics. Preferably, vehicle state inputcomprises information pertaining to potential noise sources at avehicle, and user preference input comprises a user's desire for anoise-reduction mode. The various inputs can be used to select a PWMparameter that can reduce PWM related noise when desired by a user.Furthermore, methods of the invention can include efficiently enteringnoise-reduction modes under predetermined conditions, and operating indefault modes otherwise, thereby reducing the losses incurred at highswitching frequencies, unlike prior art systems that consistently employhigh switching frequencies regardless of vehicle state or userpreference.

Preferred embodiments rely on software to implement the methods,eliminating the need for additional or customized hardware. Flowchartsincluded herein represent control logic which may be implemented usinghardware, software, or combination of hardware and software. The logicmay be implemented using any of a number of known programming orprocessing techniques or strategies and is not limited to the order orsequence illustrated. Various functions may be performed in the sequenceillustrated, at substantially the same time, or in a different sequencewhile accomplishing the features and advantages of the invention. Theillustrated functions may be modified or in some cases omitted withoutdeparting from the spirit or scope of the present invention.

What is claimed:
 1. A system, comprising: a pulse width modulation (PWM)frequency adaptation mechanism (PFAM) configured to receive vehiclestate input during a run mode of an electric drive system (EDS) at saidvehicle, said vehicle state input comprising input pertaining to currentstatus of said vehicle or a component of said vehicle other than anelectric motor of said EDS, and in response to said vehicle state input,designate one of a plurality of PWM operational modes to be implementedat said vehicle while said EDS is in said run mode, said PFAM configuredto determine, based on said vehicle state input, a presence or anabsence of alternate audible noise (AAN) at said vehicle during said runmode, said AAN comprising other than said EDS audible noise; anapparatus coupled to said PFAM and configured to implement said PWMoperational mode, said apparatus comprising a circuit in which elementsare switched on and off by PWM performed in accordance with saiddesignated operational mode; wherein said plurality of operational modesincludes a noise reduction mode configured to reduce audible noise ofsaid EDS during said run mode, and a default mode; wherein said PFAM isconfigured to designate a default mode in response to a determinationthat said AAN is present; and wherein said PFAM is configured todesignate one of a plurality of PWM implementation strategies based onsaid designated operational mode, each said strategy comprising a typeof PWM characterized by other than frequency.
 2. The system of claim 1,wherein said plurality of strategies includes at least two of continuousPWM, discontinuous PWM, random PWM and fixed frequency PWM.
 3. Thesystem of claim 1, wherein said PFAM is configured to receive userpreference input regarding said PWM operational mode, and use said userpreference input and said vehicle state input to designate said PWMoperational mode.
 4. The system of claim 1, wherein said PFAM isconfigured to determine whether said EDS is heavily loaded, and if so,designate a loss reduction mode.
 5. The system of claim 1, wherein saidPFAM is configured to designate said noise reduction mode in response toa determination of an absence of said AAN.
 6. The system of claim 1,wherein said vehicle state input comprises engine state input, vehiclemotion input, climate control system input, window state input and audiosystem input.
 7. A system, comprising: at least one digital processor; acomputer-readable medium operatively coupled to said at least onedigital processor; having stored thereon logic for sequences ofinstructions for said digital processor, the sequences of instructions,when executed by said digital processor, cause the processor to receivevehicle state input during a run mode of an electric drive system (EDS)at said vehicle, said vehicle state input comprising input pertaining tocurrent status of said vehicle or of a component of said vehicle otherthan an electric motor of said EDS, and in response to said vehiclestate input, designate one of a plurality of pulse width modulation(PWM) operational modes to be implemented at said vehicle while said EDSis in said run mode; wherein said sequence of instructions, whenexecuted by said digital processor, cause the processor to determine,based on said vehicle state input, a presence or an absence of audiblenoise at said vehicle other than said EDS audible noise; wherein saidplurality of operational modes includes a noise reduction modeconfigured to reduce said audible noise of said EDS, and a default mode;wherein said sequence of instructions, when executed by said digitalprocessor, cause the processor to designate said noise reduction mode inresponse to a determination that said audible noise other than said EDSaudible noise is absent; wherein said sequence of instructions, whenexecuted by said digital processor, cause the processor to designatesaid default mode in response to a determination that said audible noiseother than said EDS audible noise is present; and wherein said sequencesof instructions cause said processor to designate one of a plurality ofPWM implementation strategies based on said designated PWM operationalmode, said designated PWM implementation strategy comprising a type ofPWM characterized by other than frequency.
 8. The system of claim 7,wherein said sequence of instructions, when executed by said digitalprocessor, cause the processor to designate a loss reduction mode assaid operational mode when said processor determines that said EDS isheavily loaded.
 9. The system of claim 7, wherein said vehicle stateinput comprises engine state input, vehicle motion input, climatecontrol system input, window state input and audio system input.
 10. Thesystem of claim 7 wherein said plurality of strategies includes at leasttwo of continuous PWM, discontinuous PWM, random PWM and fixed frequencyPWM.
 11. A method comprising: during a run mode of an electric drivesystem (EDS) at a vehicle, receiving at a pulse width modulation (PWM)frequency adaptation mechanism (PFAM), vehicle state input related to acurrent status of a vehicle component other than an electric motor of(EDS) of said vehicle; in response to said vehicle state input, saidPFAM designating one of a plurality of PWM operational modes for PWMswitching in a circuit configured to provide a voltage to an electricmotor at said vehicle during said run mode, said plurality ofoperational modes comprising a noise reduction mode configured to reduceaudible noise of said EDS during said run mode, and a default mode;wherein said PFAM is configured to designate, based on said designatedoperational mode, one of a plurality of PWM strategies to be implementedduring said designated operational mode, each said strategy comprising atype PWM characterized by other than frequency; and wherein said PFAM isconfigured to determine, based on said vehicle state input, a presenceor an absence of alternate audible noise (AAN) at said vehicle duringsaid run mode, said AAN comprising other than said EDS audible noise,and to designate said default mode in response to a determination thatsaid AAN is present.
 12. The method of claim 11, wherein said PFAM isconfigured to designate a loss reduction mode.
 13. The method of claim11, further comprising receiving user input regarding said operationalmode preference for a default PWM operational mode.
 14. The method ofclaim 11 wherein said designating a PWM operational mode comprisesdesignating a noise reduction mode in response to said vehicle stateinput indicating said vehicle speed is changing and determining anabsence of alternative noise source at said vehicle.
 15. The method ofclaim 11, wherein said designating a PWM operational mode comprisesdesignating a loss reduction mode in response to said vehicle stateinput indicating said vehicle is traveling at a low speed, and anelectric drive system at said vehicle is heavily loaded.
 16. The methodof claim 11, wherein said selecting a PWM operational mode comprisesselecting a noise reduction mode in response to vehicle state inputindicating that said vehicle is traveling at low speed and determiningan absence of alternative noise at said vehicle.
 17. The method of claim11, wherein said PWM implementation strategy for a loss reduction modecomprises low frequency random PWM.
 18. The method of claim 11, whereinsaid PWM implementation strategy for a noise reduction mode comprises arandom strategy performed at a high frequency.
 19. A method fordesignating a pulse width modulation (PWM) parameter, comprising: apulse width modulation (PWM) frequency adaptation mechanism (PFAM)receiving vehicle state input during a run mode of an electric drivesystem (EDS) at said vehicle, said vehicle state input comprising inputpertaining to current status of said vehicle or a component of saidvehicle other than an electric motor of said EDS, wherein said PFAM, inresponse to said vehicle state input, is configured to designate one ofa plurality of PWM operational modes to be implemented at said vehiclewhile said EDS is in said run mode, said plurality of operational modesincluding a noise reduction mode configured to reduce audible noise ofsaid EDS during said run mode, and a default mode, said PFAM configuredto determine, based on said vehicle state input, a presence or anabsence of alternate audible noise (AAN) at said vehicle, said AAN beingaudible noise other than said EDS audible noise, wherein said PFAM isconfigured to designate a default mode in response to a determinationthat said alternative audible noise is present said PFAM configured todesignate one of a plurality of PWM implementation strategies based onsaid designated operational mode, each said strategy comprising a typeof PWM characterized by other than frequency; said PFAM determiningwhether a vehicle window is open, and in response to an open window,selecting a default mode and concluding said method, otherwisecontinuing with said method; said PFAM determining whether a vehicle airconditioner is operating, and in response to an operating airconditioner, selecting said default mode and concluding said method,otherwise continuing with said method; said PFAM determining whether avehicle radio is turned on, and in response to an on state for saidradio, selecting said default mode and concluding said method, otherwisecontinuing with said method; said PFAM determining whether a vehicle isin a drive mode, and in response to a vehicle not being in a drive mode,selecting said default mode and concluding said method, otherwisecontinuing with said method; said PFAM determining whether said vehicleis accelerating or decelerating, and in response to said vehicleaccelerating or decelerating, selecting a noise reduction mode andconcluding said method, otherwise continuing with said method; said PFAMdetermining whether said vehicle is moving at a low speed, and inresponse to said vehicle not moving at a low speed, designating saiddefault mode and concluding said method, otherwise proceeding with saidmethod; and said PFAM determining whether an electric drive system (EDS)of said vehicle is heavily loaded, and in response to said EDS beingheavily loaded, selecting a loss reduction mode, and in response to saidEDS not being heavily loaded selecting a noise reduction mode.